The use of bacteria with a signal-generating metabolic activity as indicators of toxicity is well established. UK patent number GB 2005018 describes a method of assaying a liquid sample for toxic substances which involves contacting a suspension of bioluminescent microorganisms with a sample suspected of containing a toxic substance and observing the change in the light output of the bioluminescent organisms as a result of contact with the suspected toxic substance. Furthermore, a toxicity monitoring system embodying the same assay principle, which is manufactured and sold under the trademark Microtox®, is in routine use in both environmental laboratories and for a variety of industrial applications. A toxicity assay using bioluminescent bacteria which have been killed, as by radiation, is described in International Patent Application Number WO 95/10767.
Although the methods and reagents utilized previously in systems such as the aforementioned Microtox® system are sensitive and reliable indicators of the presence of toxic substances, there still exists a need to provide reagents and assays having even greater sensitivity than those used heretofore.